Achievements are found in all Xbox 360 games. Dead Rising's achievements are often tied to rewards. These rewards can be found in bags on the opposite side of the air-vent entrance and in other areas found in the security room.

If you have unlocked the achievement before but not complete the game(died or reset) the screen will say it has been unlocked and that gives you a chance to earn the reward, but you still have to get one of the endings.